Friday, February 24, 2012

Intolerable, Horrible, and Derisible-Measuring Time

Intolerable, Horrible, and Derisible

     Somehow, I ended up answering two seperate questions from two different people when I started my research for this week's blog.  My husband wanted to know why some months have 30 days, and others don't.  Then my mother asked me why the date of Easter changes every year when most holidays have a set date.  When I started looking for the answer to my husband's question, I inadvertently fell upon the answer to my mother's as well.

     Most of the world today follows the Gregorian calendar, but how did we end up with this way of measuring time?  And what did we use before?  Why did we switch?  You may have noticed in previous posts that I mentioned the Julian calendar.  Before we began using the current calendar, much of western Europe used the Julian calendar.  We need to examine the history of the Julian calendar to understand the Gregorian calendar, so here goes.

     The early Roman calendar was based on the moon.  It had 304 days broken into 10 months.  Mars (March), Maius (May), Quintilis (July), and October had 31 days, and the rest had 30.  The year started in Mars and ended in December.  No one is sure what was done about the other 60-61 days .  Around 715 BC, King Numa added January and February, though in reverse order.  He also changed the number of days in each month to bring the total to 355.

     The Roman calendar was deeply flawed, and became even more so over time as the pontifical college ( the officials elected to manage the calendar) manipulated it to benefit themselves.  Julius Caesar spent some time in the pontifical college before he became caesar.  He knew about the flaws and corruption, and made the calendar a priority of reform.  He called on the Alexandrian mathematician and astronomer, Sosigenes, for help.  Sosigenes recommended switching from a lunar year to a solar (sun) year, setting the year at 365 1/4 days, and adding a day every four years.  Unfortunately, Julius was assassinated before the reforms were fully instituted, and there was some confusion.  It wasn't until 9 B.C. (some 30 years after Julius), that Augustus fixed the calendar. 
     As Christianity spread from the Middle East into Europe, new flaws in the Julian calendar began to show.  Some Christians objected to the "pagan" names for the days and months.  Others felt that the ever shifting dates of holidays were a problem.  Many objected to the new year starting in March because this was also a "pagan" tradition. Still others felt that the way we numbered years needed to be changed to reflect the birth of Christ.  An Abbot named Dionysus Exiguus was the leader of this movement.  After much research, he felt he had discovered the exact date of Christ's crucifixion, and could also determine the exact date of his birth.  He then set the date of his birth as 1 A.D. and changed the way years were recorded before that date to B.C.  Dionysus didn't realize that his calculations were off by about 4 years though.  Christ was actually born in what we now call 4 B.C.  By the 11th century though, this method was commonly accepted, and still used today. 

     Despite the various flaws in the Julian calendar, it was the most widely used in Europe, and it was accepted by the church, which was all important at the time.  One major flaw became more apparent over time though.  Sosigenes set a year as 365.25 days, when it was actually 365.24219 days.  A little over 11 minutes in the course of a year isn't much, but over time it can really throw things off.  Even with a leap year every four years, the calendar was ending up a whole day off every 128 years.  More importantly, Easter was getting later every year.  Scholars began to send suggestions to the Pope, including Roger Bacon in the 1200s.  He called the Julian calendar, "Intolerable, horrible, and derisible."

     As astronomy became more accurate, the appeals for reform increased.  Various attempts at reform failed though, until Pope Gregory XIII in 1572.  He hired astronomer Ignazio Danti, and studied the work of Lilio, along with many of the suggestions scholars had been sending.  Armed with the information he collected, he set out to have a new calendar created.  On February 24, 1582, after 10 years of study and debate, Gregory signed the new calendar into effect.  There were still complaints, especially with the calculation of the date for Easter, but the Gregorian calendar slowly began to catch on.  I say slowly because some countries didn't adopt the calendar until the 20th century.  The American colonies switched in 1752. 

                                                         Thirty days hath September,
                                                         April, June, and November.
                                                         All the rest have thirty-one
                                                         Excepting February alone,
                                                         To which we twenty-eight assign
                                                        ‘til Leap Year makes it twenty-nine.
                                                                                   Anonymous 1500s

     So what did the Gregorian calendar change?  It set the dates for the equinoxes and solstices.  January 1 became the date of the new year.  Most holidays were given a specific date.  Leap year added a day to February to years that were divisible by four, except for years that end in 00, which must be divisible by 400.  While not perfect, the flaws are minor, and will only be obvious 10,000 years from the beginning of the calendar. 

     But what about Easter you say?  Well, it's not a simple explanation, and it involves a lot of math and astronomy, and even a little spirituality.  I will go a little deeper into Easter in April, but for now, here is the basic way of figuring out the date for Easter in the Gregorian calendar system: Easter must occur between March 22 and April 25.  It happens on the first Sunday after the full moon on or after the spring equinox.  Here is the catch though, it doesn't have to be a real full moon.  The date of the full moon is decided by an table of ecclesiastical numbers, and may not coincide with the real phases of the moon.  This was one of the problems that the church had with Gregory's calendar, and is still very confusing to people today.  For more about Easter, check back on April 7. 

From the Roman calendar, to the Julian calendar, to the Gregorian calendar, attempts to measure time have revealed that it's not a simple task.  Many other types of calendars have been used around the world.  Some are lunar, some are solar, and some use their own unique methods.  What is clear is that people like to keep track of time.